A wing of aircraft is designed so that the wing shape becomes optimum upon cruising which takes the longest time in flight routes. Namely, the wing is designed so that, upon cruising, a lift force can be obtained to the extent of the weight at high airspeeds; and a drag becomes as small as possible.
Meanwhile, a lift force becomes larger as an airspeed, and an angle of attack or an airfoil camber becomes larger. Accordingly, during low-airspeed flight at the time of takeoff and landing or at the time of turning, a wing's angle of attack is made larger or a wing shape is bent greatly at a hinge portion, with which a wing is provided, in order to obtain a higher lift force. However, when the wing's angle of attack increases beyond the limit, or when the airfoil camber becomes larger too much, a flow separates from a wing surface so that a drag becomes larger and additionally no sufficient lift force can be obtained, and thereby there is a fear that the maneuverability might degrade.
Hence, in order to suppress the flow separation that occurs at a wing surface upon takeoff and landing when a wing's angle of attack or an airfoil camber becomes larger, a vortex generator is placed on a wing surface of aircraft. The vortex generator generates a longitudinal vortex from a certain position on the wing surface, mixes a larger-momentum flow on the outer side of the boundary layer with a slow flow on the wing surface, and thereby increases the momentum of the flow on the wing surface to suppress the occurrence of the separation.
An ordinary vortex generator, which have been employed in aircraft, comprises a plate-shaped body with a rectangular or trapezoidal shape, and the like, and is placed in such a state that the plate surface is directed obliquely so that a flow runs into the plate surface and additionally the plate surface rises substantially perpendicularly with respect to a wing surface. Note that, in large-sized aircraft applications, the length of the rising plate-shaped body is about 55-75 mm, the height is about 20-23 mm, and the thickness is about 2 mm; and that these plate-shaped bodies are placed forward on a control surface at intervals in the lateral direction (or in the span direction of the wing) in a quantity of a plurality of pieces.
By the way, while a vortex generator demonstrates such a function that it suppresses a flow separation from a wing surface upon takeoff and landing when a wing's angle of attack or an airfoil camber becomes larger, there is a disadvantage that, upon cruising when a wing's angle of attack or an airfoil camber becomes smaller, it has disturbed a flow on a wing surface by means of vortexes generated by the vortex generator and has enlarged a drag by means of turbulent flow. The phenomenon that, upon cruising which takes the longest time in flight routes, a drag has been enlarged by means of the vortex generator results in a greater problem from the viewpoint of the maneuvering performance and fuel consumption of aircraft.
Hence, techniques have been known, techniques which adjust the modes of vortex generators depending on flying circumstances.
For example, in Patent Literature No. 1 (or Japanese Unexamined Patent Publication (KOKAI) Gazette No. 5-16,892), a separation controlling apparatus is disclosed; as illustrated in FIG. 18, it is equipped with: a sensor 82 for detecting the states of fluidic flow on a wing surface 81 of a wing 80, the flow rates of fluid, vortexes which occur in fluidic flows; data-processing means 83 comprising a CPU, or the like, which analyzes the states of separation based on sensor signals and additionally outputs control signals depending on the states of separation; driving means 84, such as a piezoelectric actuator, or the like, which is actuated by the control signals from the data-processing means 83; and a vortex generator 86 whose leading-end position 85, with respect to the wing surface 81 making a boundary to flows, is made ascendable and descendable by means of the driving means 84.
In this separation controlling apparatus, the states of fluidic flow on the wing surface 81, and the like, are detected with the sensor 82; and then the driving means 84 is actuated by means of the control signals from the data-processing means 83, control signals which depend on the states of separation based on the sensor signals; and thereby the leading-end position 85 of the vortex generator, which is disposed with respect to the wing surface 81, is moved and adjusted. Thus, when no separation occurs on the wing surface 81, the leading-end position 85 of the vortex generator 86 is put into such a state that it retracts within the wing 80; on the other hand, when separations occur on the wing surface 81, the leading-end position 85 of the vortex generator 86 is put into such a state that it protrudes from the wing surface 81 by a predetermined magnitude; and thereby it is possible to control the flow separations optimally.
Moreover, in Patent Literature No. 2 (or U.S. Pat. No. 6,427,948 B1), a vortex generator is disclosed; as illustrated in FIG. 19, it is equipped with a body 90, a blade spring 91 which is formed as a bow shape in its natural state, and a heating element 92 by means of electric resistance. The body 90 is constituted of a rectangle-shaped base portion 93, which is fixed onto awing surface, and a rectangle-shaped fin portion 94, which is connected with a side surface on a one-end (or front-end) side of the base portion 93 integrally and additionally which has a rise surface rising from the base portion 93 perpendicularly. And, the fin portion 94 comprises a shape memory alloy, and a shape-memorized configuration of this shape memory alloy is not a bow shape, but is such a configuration that it extends linearly so that the rise surface of the fin portion 94 becomes flat. Moreover, the fin portion 94 is made deformable into a bow shape so that, at a temperature of the transformation finish temperature or less, it follows along the bow shape of the blade spring 91. Accordingly, at a temperature of the transformation finish temperature or less, the blade spring 91's engagement clip portions 91a and 91b are fitted into the fin portion 94's front edge 94a and rear edge 94b, and thereby the fin portion 94 is formed as a configuration, which is deformed to such a bow shape that follows along the bow shape of the blade spring 91, by means of the blade spring 91's spring force. Moreover, the heating element 92, to which electricity is supplied through conducting wires 95 and 96 and which heats the fin portion 94 by means of electric resistance, is bonded onto the rise surface of the fin portion 94.
Accordingly, in this vortex generator, since the fin portion 94 is formed as a bow shape by means of the blade spring 91's spring force when being a transformation finish temperature or less of the shape memory alloy, it generates vortexes on the wing surface to suppress the flow separations. On the other hand, the fin portion 94 is turned into the shape-memorized linearly-extended configuration against the blade spring 91's spring force when being heated to a reverse transformation finish temperature or more by means of the heating element 92. Since the linearly-extended fin portion 94 extends parallelly along the flow of fluid, no vortex arises on the wing surface so that it is possible to restrain the drag enlargement resulting from turbulent flows. Therefore, in this vortex generator, the fin portion 94's shape is changed by controlling the electricity supply to the heating element 92, and thereby it is possible to control the flow separations optimally.
Note that, in this vortex generator, the fin portion 94 returns to the bow shape by means of the blade spring 91's spring force when the electricity supply to the heat element 92 is broken off, due to the electric-system failures, and the like, so that the temperature of the fin portion 94 drops below the transformation finish temperature. Accordingly, in this vortex generator, even if no electricity cannot be supplied to the heating element 92 because of certain reasons, since it is possible to have the separation suppressing function of the fin portion 94 demonstrate by turning the fin portion 94 into the bow shape by means of the blade spring 91, a fail-safe mechanism works. However, in this instance, since the fin portion 94 has come to generate vortexes on the wing surface even upon cruising, it brings about the enlargement of drag.
However, according to the prior art set forth in aforementioned Patent Literature No. 1, the sensor 82, which detects the states of fluidic flow, and the like, on the wing surface 81, the data-processing means 83, which comprises a CPU, or the like, and the driving means 84, such as a piezoelectric actuator, or the like, which actuates the vortex generator 86, are required.
Moreover, according to the prior art set forth in aforementioned Patent Literature No. 2, the temperature of the fin portion 94, which comprises a shape memory alloy, is adjusted by means of controlling the electricity supply to the heating element 92, and thereby the form of the fin portion 94 is changed. Further, in this prior art, when trying to change the form of the fin portion 94 securely between upon takeoff and landing and upon cruising, a sensor for judging the timing of the change, and data processing means therefor have come to be needed.
Accordingly, the techniques set forth in aforementioned Patent Literature Nos. 1 and 2 require an energy supply from the outside, and are consequently associated with such problems that their apparatuses are complicated structurally; failures are likely to occur in the electric systems, and the like; and moreover their repairs and maintenance as well as their installations to existing wings are troublesome.